Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$139.38	10.590%	$154.1403	$154.14	$154.15	$154.10
Purchase #2	$243.77	12.252%	$273.6367	$273.64	$273.65	$273.60
Purchase #3	$192.72	5.706%	$203.7166	$203.72	$203.70	$203.70
Purchase #4	$6.36	12.503%	$7.1552	$7.16	$7.15	$7.20
Purchase #5	$88.62	12.253%	$99.4786	$99.48	$99.50	$99.50
Purchase #6	$190.35	10.656%	$210.6337	$210.63	$210.65	$210.60
Purchase #7	$38.65	13.308%	$43.7935	$43.79	$43.80	$43.80
7 purchase totals =	$899.85		$992.5546	$992.56	$992.60	$992.50